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Arctic charr

The Arctic charr, (Salvelinus alpinus), is closely related to two other native species: the Atlantic salmon and the brown trout. There is good evidence that Arctic charr were the first of the species to colonise the new post-glaciation freshwaters of Scotland it can be said that Arctic charr is the aboriginal freshwater fish species of Scotland. In Scotland, all known Arctic charr populations in Scotland are now freshwater-resident, however these have been derived from anadromous invaders which colonised these habitats as the ice receded. It is interesting to note that Arctic charr populations located at latitudes higher than 65o N continue to exhibit anadromous behaviour patterns when access to marine habitats are available. Populations at lower latitudes remain in freshwaters for their entire life-cycle.

Where are they found?

As its name suggests, the Arctic charr is a holarctic species which occurs in lakes and rivers throughout the northern hemisphere The most southerly natural populations in Europe are found at altitude in the Rhine and Danube catchments. They have, however, been introduced to many Alpine lakes and to lakes in the Pyrenees.

Arctic charr have the most northerly distribution of any freshwater fish and, in some northern latitudes the freshwater fish community is comprised entirely of this species. Globally there are thought to be around 50,000 populations of Arctic charr, most of these (~30,000) are located in Norway. The distribution of Arctic charr within the British Isles is polarised towards northern upland areas. Scotland is a stronghold for Arctic charr within the British Isles and 258 Scottish lochs are known to contain this species. Their distribution throughout the remainder of the British Isles is patchy, with 74 Irish populations and localised populations in north-west England (8) and north Wales (4).

What sort of habitats do they use?

In Scotland, there are no known populations that exhibit anadromy, although we cannot not rule out the possibility that this may occur. There are no known populations in Scotland which occupy rivers throughout their life cycle, however there some populations that are found there occasionally and a few populations are known to spawn in streams and rivers of systems which also contain standing waters. Thus the majority of Arctic charr populations in Scotland occupy standing waters.

Are they exploited?

There are no commercial or subsistence fisheries for Scottish Arctic charr populations and it is only rarely exploited for angling, except by a very small number of specialist anglers or where it is a by-catch for other salmonid species. This contrasts significantly with other countries, where there are both significant commercial and sport fisheries. Thus the evidence suggests that in comparison with other countries the Arctic charr populations of Scotland have not been substantively modified by between-population mixing. This means that, unlike many European populations, most Scottish Arctic charr populations are genetically pristine.

Status in Scotland and threats

Potential threats to Arctic charr include climate change, eutrophication, acidification, afforestation, lake engineering, exploitation, aquaculture, non-native species introductions and introductions of charr of different race, stock or type. In Scotland in contrast, the number of extinctions of populations in historical times, is relatively low (although it is likely that some populations became extinct before records were available). We know of a number of sites were Arctic charr have been lost, and there may be others where populations are on the brink of extinction. The majority of known extinctions are from south and central Scotland and at least five are thought to be due to acidification.

The Arctic charr 'complex' and the conservation conundrum

It has long been recognised that Arctic charr display an unusually high degree of variance in phenotype (i.e. physical characteristics). This variation manifests over a wide range of characteristics including: morphology, size, colouration, behaviour and life history. Considerable variation can take place between (allopatric) and within (sympatric) Arctic charr populations. Arctic charr can differ markedly between waterbodies, but in some lochs up to three genetically and morphologically different forms can be found. Each of these may exhibit different patterns of habitat use, spawning location and the timing of reproductive behaviour. These populations are therefore 'reproductively isolated' and this, in turn, leads the way to genetic divergence.

Such is the variation with Arctic charr populations within the British Isles that taxonomists in the early 20th century described the existence of 15 different 'charr' species - seven of which were present in Scotland. It is now accepted that these fish are all variants of one species, the Arctic charr S. alpinus. There have been recent moves by some individuals within the scientific community, however, to revise the taxonomy of Arctic charr and 'split' this species into a number of individual species units - based entirely on their morphology. This approach ignores evidence that Arctic charr in northern Europe are currently undergoing a period of very rapid evolutionary change resulting in a very significant adaptive radiation.

If this new taxonomy is accepted, the addition of an 12 new 'species' of charr to Scotland (with many more to come if the same approach is used in future years) will carry with it significant consequences for freshwater fish conservation both nationally, and internationally. It is clear that much further investigation, using genetic approaches, is required before this new, and potentially costly, taxonomy is accepted - not one which is based not only on the morphological characteristics of a rapidly evolving and phenotypically plastic species.

Current levels of protection

Currently, Arctic charr are a conservation feature in five Sites of Special Scientific Interest (Lochs Eck, Insh, Builg, Girlsta and Doon), they are also present in a number of waterbodies protected for other purposes, either under the Natura 2000 network or the National Nature Reserve series. The considerable conservation value of Arctic charr within the UK has been further recognised by their addition to the UKBAP Priority Species List in 2007.